USB Standards

USB standards

USB 1.1

USB 1.1, introduced in 1995, is the original USB standard. It has two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much lower bandwidth.

USB 2.0

In 2002, a newer specification, USB 2.0, or Hi-Speed USB 2.0, gained wide acceptance in the industry. This version is both forward- and backward-compatible with USB 1.1. It increases the speed of the peripheral to PC connection from 12 Mbps to 480 Mbps, or 40 times faster than USB 1.1!

This increase in bandwidth enhances the use of external peripherals that require high throughput, such as CD/DVD burners, scanners, digital cameras, video equipment, and more. USB 2.0 supports demanding applications, such as Web publishing, in which multiple high-speed devices run simultaneously. USB 2.0 also supports Windows® XP through a Windows update.

It has the flat USB Type A plug, but inside there is an extra set of connectors and the edge of the plug is blue instead of white. The Type B plug looks different with an extra set of connectors.

The cable

The USB 3.0 cable contains nine wires, four more than USB 2.0, which has one pair for data and one pair for power. USB 3.0 adds two more data pairs, for a total of eight plus a ground. These extra pairs enable USB 3.0 to support bidirectional asynchronous, full-duplex data transfer instead of USB 2.0's half-duplex pollling method.

More Power

USB 3.0 also provides 50% more power than USB 2.0 (150 mA vs 100 mA) to unconfigured devices and up to 80% more power (900 mA vs 500 mA) to configured devices. It also conserves power too compared to USB 2.0, which uses power when the cable isn’t being used.